This invention relates generally to valves and, more specifically, to weir-type diaphragm valves.
Diaphragm valves have been in common use for many years. Diaphragm valves are most commonly used in applications where contact between the flowing fluid and the interior materials within an ordinary valve are not compatible. Accordingly, diaphragm valves are frequently used where the flowing fluid is corrosive to the interior parts of ordinary valves or where the flowing fluid might be contaminated by contact with the interior parts of ordinary valves.
One of the most common types of diaphragm valves are weir-type diaphragm valves. In this type of diaphragm valves, the flowing fluid within the valve flows over a generally vertical weir disposed transverse to the flow path within the valve. An elastomeric diaphragm is affixed in a generally horizontal position spaced apart from the top of the weir. When the valve is to be closed, a vertical plunger disposed above the diaphragm is operated to press down upon the diaphragm so as to seal the diaphragm against the top of the weir. In such weir-type diaphragm valves, a transverse bead is commonly disposed on the underside of the diaphragm in such a way that the bead mates with the top of the weir. This is illustrated in FIGS. 4-7 of the drawings. It has been found that diaphragms having such a transverse bead provide a more positive seal than do diaphragms without a transverse bead.
Unfortunately, there is a problem with the use of such prior art weir-type diaphragm valves having a transverse bead on the underside of the diaphragm. Because the diaphragm is made from an elastomeric material, fluid pressure against the bead when the valve is in the closed position tends to push the bead in the downstream direction. The elastomeric material in the upstream portion of the diaphragm is stretched, while the elastomeric material within the downstream portion of the diaphragm is compressed. Where the fluid pressure is relatively high and/or after repeated uses of the valve in the closed position, the transverse bead can be displaced off of the top of the weir altogether, as illustrated in FIG. 7. When this occurs, the diaphragm no longer adequately seals against the top of the weir in the closed position, and the valve leaks.
Accordingly, there is a need for a weir-type diaphragm valve which avoids this problem with prior art weir-type diaphragm valves in a simple and relatively inexpensive manner.
The invention satisfies this need. The invention is a weir-type diaphragm valve comprising a valve body, a flexible diaphragm and a valve stem and handle assembly. The valve body has an inlet end, an outlet end and an internal flow pass therebetween. A weir having an upstream face, a downstream face and a top edge is disposed transverse to the flow path. The top edge of the weir provides a valve seat having a raised transverse bead running substantially the entire length, along the top edge of the weir. The diaphragm is disposed above the valve seat. The diaphragm can be alternatively flexed between a closed diaphragm position, wherein the diaphragm is in tight abutment with the valve seat, and an open diaphragm position wherein the diaphragm is spaced apart from the valve seat. The valve stem and handle assembly is adapted to alternatively flex the diaphragm between the closed diaphragm position and the open diaphragm position.
By constructing the diaphragm valve with the bead rigidly disposed along the valve seat (instead of on the underside of the elastomeric diaphragm), the invention successfully avoids the leaking problems of prior art diaphragm valves.